Ground fault circuit interrupters (GFCI) for interrupting the flow of electrical power to a device upon the occurrence of a ground fault have been known for many years. Known devices are usually effective in detecting ground faults associated with damaged insulation on the line conductor that could lead to fire, or to current accidentally flowing through a human body that could cause electrocution. In general, a GFCI senses and/or responds to a condition in a line carrying electrical current which indicates a presently or imminently dangerous condition, such as the presence of a current path other than the intended path of normal operation. Response to the sensed dangerous condition may be in the form of alarm actuation and/or opening the line (interrupting the circuit) between the source of power and the load.
Heretofore, GFCI's have been designed to self test in the event of a failure of the device to provide the intended protection. Among these are U.S. Pat. No. 5,600,524 (Neiger) that includes a timer that initiates a periodic self test of the GFCI, or that initiates a periodic alarm to alert the user to manually push the test button on the GFCI, utilizing circuitry that adds cost and that takes up space within the confines of a duplex receptacle embodiment. Another type of self test is disclosed in U.S. Pat. No. 5,638,243 (Torezan) which makes use of a visual indicator to display if hot and neutral power source conductors are inadvertently miswired to the load terminals of the GFCI, such that GFCI protection is lost at the duplex receptacles on the face of the GFCI. However, self-test of the electrical circuit is not disclosed. In addition, the self-test method does not disclose lock-out of load side power by the GFCI's interrupting contacts and the user is obliged to correctly interpret and take action based on appearance of the visual indicator. Similarly, U.S. Pat. No. 5,715,125 (Neiger) addresses self-testing of the relay solenoid which serves to open the GFCI interrupting contacts, but does not disclose self-test of the electrical circuit. Yet another type of self test is disclosed in U.S. Pat. No. 6,040,967 (DiSalvo), wherein the failure of certain components such as the SCR results in locking out power to the load.
However, other types of failures such as those involving the GFCI sensing circuitry require pushing the test button to initiate lock-out. In response, the GFCI trips out, after which the user resets the GFCI. Although regular testing is encouraged, in reality, few users test their GFCI's on a regular basis. Therefore, there is a need for a GFCI with a self-test feature.